1. Field of the Invention
The present invention is directed to a gating and target device, herein also referred to as spot film device, for use in an x-ray examination apparatus, and in particular to such a device including a secondary radiation diaphragm comprising two moveable diaphragm plates, a scattered ray grid, and an x-ray film cassette holder.
2. Description of the Prior Art
Spot film devices which also include a holder for an xray film cassette and a scattered ray grid are known in the art as described, for example, in German OS No. 28 42 659. This device includes a secondary radiation diaphragm consisting of two diaphragm plates and a means for moving the diaphragm plates in respective parallel planes toward and away from each other to adjust the size of the opening formed by the combination of the respective opening limited by the diaphragm plates. The scattered ray grid in this device is disposed in a plane parallel to the respective planes in which the diaphragm plates are disposed, so that the diaphragm plates and the scattered ray grid occupy successive planes between a wall of the device against which the examination subject lies, and the x-ray film cassette holder. Thus a relatively large distance exists between an examination subject, of whom an image is to be obtained, and the plane in which the film of the x-ray film cassette is disposed. This large distance has a disadvantageous effect on the quality of the x-ray exposure of the examination subject because, as is known, unsharpness of the exposure increases with increasing distance between the subject and the film plane.